Floating cup pump having swashplate mounted cup elements

ABSTRACT

A floating cup pump assembly incorporating a tilted swashplate structure with cup elements projecting away from either side of the swashplate structure. The swashplate structure is positioned between a first group of matedly engaged piston elements and a second group of matedly engaged piston elements. The piston elements rotate around a first axis and the cup elements rotate around a different axis causing the cups to reciprocate relative to the piston elements.

TECHNICAL FIELD

This patent disclosure relates generally to pump assemblies and, moreparticularly, to floating cup pump assemblies utilizing a plurality ofpiston elements disposed around a first rotating surface and a pluralityof complimentary cup elements disposed around a second rotating surfacein angled relation to the piston elements. The cup elements reciprocaterelative to the piston elements during rotation.

BACKGROUND

Pumping devices utilizing a plurality of piston elements mounted arounda first rotor and a plurality of complimentary cup elements projectingaway from a swash plate in angled relation to the piston rotor aregenerally known. United States Patent Application No. 2006/0222516 inthe name of Achten, having a publication date of Oct. 5, 2006, disclosesone such device. Embodiments of pumps described in this referenceinclude a centrally disposed rotor having a plurality of pistonsprojecting away from both sides of the rotor. A pair of cooperating drumplates disposed outboard from the rotor support an arrangement of cupelements or drum sleeves adapted to house distal portions of thepistons. The rotor supporting the pistons rotates around a first axis ofrotation. The drum plates rotate in angled relation to the first axis.The rotor supporting the pistons is rotated in tandem with the drumplates during operation. Due to the angle between the rotor and the drumplates, the cups are caused to stroke along the length of thecorresponding piston elements such that the volume occupied by thepiston elements is alternately increased and decreased during therotational cycle. Thus, fluid introduced into a cup element when thecomplimentary piston is in a substantially withdrawn position may bepressurized and expelled as the cup is pushed inwardly during therotational cycle.

In the noted reference, each of the drum plates housing the cup elementsrotates around a convex centering surface or ball guide. In order tobalance forces generated within the pump, the drum plates on either sideof the central rotor are mounted and operated with substantial symmetry.A lack of symmetry leads to the pump operating in an unbalancedcondition. Such unbalanced operation may degrade performance andintroduce stresses which can cause damage. The need to maintain asubstantially matched arrangement of drum plates in the prior devicegives rise to a relatively complex initial construction process toensure the desired matched angle and spacing on each side of the centralrotor. Carrying out this initial construction may require a relativelyhigh level of skill. Accordingly, an alternative construction whichpromotes balanced operation while reducing complexity is desirable.

BRIEF SUMMARY

The disclosure describes, in one aspect, a floating cup pump structurehaving a swashplate structure including a first side and an opposingsecond side facing away from the first side. A first plurality of cupelements projects away from the first side of the swashplate structureand a second plurality of cup elements projects away from the secondside of the swashplate structure. The swashplate structure is positionedbetween a first group of piston elements mounted on a first rotatablepiston support and a second group of piston elements mounted on a secondrotatable piston support. At least one member of the first group ofpiston elements is adapted to engage a complimentary cup elementprojecting away from the first side of the swashplate structure. Atleast one member of the second group of piston elements is adapted toengage a complimentary cup element projecting away from the opposingside of the swashplate structure. The swashplate structure is angledrelative to at least one of the rotatable piston supports.

In another aspect, this disclosure describes a method for pumping afluid. The method includes providing a fluid to a pump having a tiltedswashplate structure. A first plurality of cup elements projects awayfrom a first side of the swashplate structure and a second plurality ofcup elements projects away from a second side of the swashplatestructure facing away from the first side. The first plurality of cupelements engages a first plurality of piston elements and the secondplurality of cup elements engages a second plurality of piston elements.At least a portion of the fluid is introduced into the first pluralityof cup elements and the second plurality of cup elements. The firstplurality of cup elements and the second plurality of cup elements arereciprocated relative to the engaged piston elements, and the fluid isexpelled in a pressurized state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away schematic view illustrating components of anexemplary floating cup pump assembly consistent with this disclosure;

FIG. 2 is an exploded schematic assembly view illustrating a curvedsurface support element relative to a rotatable shaft assembly as may beused in the exemplary floating cup pump assembly of FIG. 1; and

FIG. 3 is a cut-away schematic view illustrating a distal portion of apiston element at the interior of a cooperating cup element.

DETAILED DESCRIPTION

This disclosure relates to a floating cup pump assembly incorporating aswashplate structure with cup elements projecting away from a first sideand an opposed second side of the swashplate structure. The swashplatestructure is positioned between a first group of engaged piston elementsand a second group of engaged piston elements. The swashplate structureis tilted to define angled backing support surfaces for carrierssupporting the cup elements. The piston elements rotate around a firstaxis and the carriers supporting the cup elements follow the rotationalmovement of the piston elements. Due to the angled backing supportprovided by the swashplate structure, the cups are pushed around asecond axis in angled relation to the first axis thereby causing thecups to reciprocate relative to the piston elements.

Reference will now be made to the drawings, wherein like referencenumerals designate like elements in the various views. FIG. 1illustrates a pump assembly 10 adapted to be mounted within a housing11. In this exemplary construction, a rotatable shaft assembly 12extends along a first axis 13. The rotatable shaft assembly 12 isadapted for rotation around the first axis 13 by use of an engine orother external power source. As illustrated in FIGS. 1 and 2, theexemplary pump assembly 10 includes a swashplate structure 14 in theform of a disk or plate structure. As shown, the swashplate structure 14is mounted in tilted orientation relative to the rotatable shaftassembly 12. In this regard, the swashplate structure 14 is mountedaround the rotatable shaft assembly 12 by a bearing connection 16 or thelike such that swashplate structure 14 may tilt or wobble in a directioncorresponding generally to the first axis 13 during operation asrepresented by the double arrows and as will be described more fullyhereinafter.

In the exemplary construction illustrated in FIG. 1, the swashplatestructure 14 defines a backing support for an arrangement of first cupelements 18 having openings projecting away from a first face of theswashplate structure 14 and an arrangement of second cup elements 19projecting away from a second face of the swashplate structure 14. Inthe illustrated construction, the arrangement of first cup elements 18is mounted on a first carrier plate 44 disposed adjacent to the firstface of the swashplate structure 14. The arrangement of second cupelements 19 is mounted on a second carrier plate 45 disposed adjacent tothe second face of the swashplate structure 14. The first carrier plate44 and the second carrier plate 45 are substantially free-floating suchthat the arrangement of first cup elements 18 and the arrangement ofsecond cup elements 19 may move circumferentially during operation aswill be described further hereinafter.

As shown, the first cup elements 18 matedly engage distal portions of aplurality of complementary first piston elements 20. The second cupelements 19 matedly engage distal portions of a plurality ofcomplementary second piston elements 21. The first piston elements 20extend away from a first rotatable piston support 22. The second pistonelements 21 extend away from a second rotatable piston support 23. Asillustrated, the first rotatable piston support 22 and the secondrotatable piston support 23 are disposed radially about rotatable theshaft assembly 12 in generally opposing relation to one another oneither side of the swashplate structure 14. According to the illustratedconstruction, the first piston elements 20 have a generally hollow,frusto-conical configuration with an increased diameter distal portionand a fluid passageway 26 running along the length from the distalportion to a proximal portion held at the first rotatable piston support22. Likewise, the second piston elements 21 have a generally hollow,frusto-conical configuration with an increased diameter distal portionand a fluid passageway 27 running along the length from the distalportion to a proximal portion held at the second rotatable pistonsupport 23. However, other suitable constructions may likewise beutilized as desired. It is to be understood that while thecross-sectional view of FIG. 1 illustrates one pair of first cupelements 18 and one pair of second cup elements 19, numerous first cupelements 18 are arranged in a circumferential pattern to project awayfrom a first side of the swashplate structure 14. Likewise, numeroussecond cup elements 19 are arranged in a circumferential pattern toproject away from an opposing second side of swashplate structure 14.Numerous first piston elements 20 are arranged circumferentially aroundfirst rotatable piston support 22 so as to matedly engage complementaryfirst cup elements 18 during operation. Numerous second piston elements21 are arranged circumferentially around second rotatable piston support23 so as to matedly engage complementary second cup elements 19 duringoperation. Although the first piston elements 20 and the second pistonelements 21 are illustrated as being in substantially aligned, opposingrelation, it is also contemplated that the first piston elements 20 andthe second piston elements 21 may be offset relative to one another ifdesired.

In the illustrated construction of FIG. 1, the first rotatable pistonsupport 22 and the second rotatable piston support 23 are operativelyconnected in substantially coaxial relation to rotatable shaft assembly12 such that rotation of rotatable shaft assembly 12 causes the firstrotatable piston support 22 and the second rotatable piston support 23to rotate about the first axis 13. However, the first carrier plate 44and the second carrier plate 45 are oriented at an angle relative to therotatable shaft assembly 12 and the first axis 13 due to the angledorientation of the swashplate structure 14 which defines a backingsupport. Accordingly, the first cup elements 18 and the second cupelements 19 supported thereon are rotatable around a second axis 15disposed in angled relation to the rotatable shaft assembly 12.

According to the exemplary construction, the first carrier plate 44 issupported radially in this angled orientation by a first curved surfacesupport element 40 alternatively referred to as a “ball guide” which isarranged about the rotatable shaft assembly 12. Likewise, the secondcarrier plate 45 is supported radially in this angled orientation by asecond curved surface support element 41. As best illustrated throughjoint reference to FIGS. 1 and 2, each of the first curved surfacesupport element 40 and the second curved surface support element 41 mayinclude a convex exterior support surface 42 adapted to engage a carrierplate 44 operatively connected across one side of the swashplatestructure 14. In the illustrated construction, the convex exteriorsupport surface 42 tapers inwardly from a base portion 46 of enhanceddiameter towards a leading edge 48 of reduced diameter such that theleading edge 48 projects generally towards the swashplate structure 14.

By way of example only, and not limitation, it is contemplated that eachof the first curved surface support element 40 and the second curvedsurface support element 41 may have a substantially unitary constructionformed by techniques such as casting, powder metallurgy, or othersuitable formation techniques using metal alloys or other materialsadapted to withstand substantial cyclical stresses. However, it islikewise contemplated that portions may be formed separately andthereafter joined together if desired. According to one contemplatedpractice, the first curved surface support element 40 and/or the secondcurved surface support element 41 may be formed separately fromcomponents of the rotatable shaft assembly 12 such that the first curvedsurface support element 40 and/or the second curved surface supportelement 41 is non-integral with the rotatable shaft assembly 12.Accordingly, the first curved surface support element 40 and/or thesecond curved surface support element 41 may be held in separablerelationship relative to the rotatable shaft assembly 12. That is, thefirst curved surface support element 40 and/or the second curved surfacesupport element 41 may be subject to nondestructive removal from therotatable shaft assembly 12 upon disassembly of the pump assembly 10. Ofcourse, the first curved surface support element 40 and/or the secondcurved surface support element 41 may also be formed in integralrelation with the rotatable shaft assembly 12 by techniques such ascasting, machining or the like.

By way of example only, and not limitation, FIG. 2 illustrates onearrangement for operative connection between the rotatable shaftassembly 12 and an independently formed curved surface support element.In the illustrated arrangement, the rotatable shaft assembly 12 includesa splined collar 50 having a pattern of ridges 52 extendinglongitudinally along a portion of the splined collar 50. The ridges 52are adapted to cooperatively engage a pattern of grooves 54 arrangedaround an interior portion of the curved surface support element.Accordingly, the curved surface support element may slide over rotatableshaft assembly 12 until engaging the splined collar 50. At the splinedcollar 50, the ridges 52 engage the grooves 54 thereby preventingrelative rotational movement between the curved surface support elementand the rotatable shaft assembly 12. However, the curved support elementmay nonetheless retain the ability to engage in some degree of slidingmovement relative to the rotatable shaft assembly 12. Of course, it isto be understood that the illustrated construction is exemplary only andthat any number of other constructions may likewise be utilized. By wayof example only, and not limitation, in one such alternative arrangementthe interlocking ridges and grooves may be reversed if desired such thatthe ridges are disposed at the interior of the curved surface supportelement with corresponding grooves being located along the splinedcollar 50.

As shown in FIG. 1, the rotatable shaft assembly 12 extends through afirst carrier plate opening 60 in the first carrier plate 44 and througha corresponding second carrier plate opening 61 in the second carrierplate 45. Each of the first carrier plate opening 60 and the secondcarrier plate opening 61 has a diameter sized to permit acceptance ofthe leading edge of the corresponding first curved surface supportelement 40 or second curved surface support element 41 without passingthe base portion. In the exemplary construction, the first curvedsurface support element 40 is continuously biased inwardly towards thefirst carrier plate opening 60 and the swashplate structure 14 by use ofa first compression spring 64 or other biasing elements disposed atpositions around the rotatable shaft assembly 12. Likewise, the secondcurved surface support element 41 is continuously biased inwardlytowards the second carrier plate opening 61 and the swashplate structure14 by use of a second compression spring 65 or other biasing elementsdisposed at positions around the rotatable shaft assembly 12. Inoperation, the first compression spring 64 and the second compressionspring 65 apply compression forces which operate along a line of forcesubstantially parallel to the rotatable shaft assembly 12 and the firstaxis 13. As shown, the first compression spring 64 or other biasingelements may operate directly against the first curved surface supportelement 40 and the first rotatable piston support 22 without the needfor intermediate structures, although such intermediate structures suchas anti-friction rings and the like may be used if desired. Likewise,the second compression spring 65 or other biasing elements may operatedirectly against the second curved surface support element 41 and thesecond rotatable piston support 23 without the need for intermediatestructures, although such intermediate structures such as anti-frictionrings and the like may be used if desired. It is also contemplated thatspacer sleeve or other spacing element may be used in place of the firstcompression spring 64 and the second compression spring 65 if desired.

In the illustrated construction, the first carrier plate opening 60 issurrounded by a first beveled or curved engagement surface 62 adapted toengage the convex exterior support surface of the first curved surfacesupport element 40 in substantially complimentary relation. Likewise,the second carrier plate opening 61 is surrounded by a second beveled orcurved engagement surface 63 adapted to engage the convex exteriorsupport surface of the second curved surface support element 41 insubstantially complimentary relation. As the rotatable shaft assembly 12rotates during operation, the first carrier plate 44 and the secondcarrier plate 45 are likewise caused to rotate due to circumferentialpushing action by the first piston elements 20 and the second pistonelements 21. During this rotation, the swashplate structure 14 does notrotate but may carry out a dynamic wobbling motion in the axialdirection as forces are applied and relieved during different stages ofthe rotational cycle. During this wobbling motion portions of the firstbeveled engagement surface 62 move axially along the first curvedsurface support element 40 and portions of the second beveled engagementsurface 63 move axially along the second curved surface support element41. Thus, the first curved surface support element 40 and the secondcurved surface support element 41 provide radial support whilenonetheless permitting the first carrier plate 44 and the second carrierplate 45 to wobble in concert with the swashplate structure 14 toaccommodate forces applied to opposing faces of the swashplate structure14 during operation.

Referring jointly to FIGS. 1 and 3, during operation of the pumpassembly 10, a fluid such as oil, hydraulic fluid, cooling fluid or thelike may be introduced through a first inlet opening 70 and a secondinlet opening 71. As shown, the first inlet opening 70 is positioned foralignment with a first fluid passageway 26 in a first piston element 20when the first piston element 20 is at a position of maximum withdrawalrelative to a corresponding first cup element 18. Likewise, the secondinlet opening 71 is positioned for alignment with a second fluidpassageway 27 in a second piston element 21 when the second pistonelement 21 is at a position of maximum withdrawal relative to acorresponding second cup element 19. As best illustrated in FIG. 3, thefirst cup elements 18 have a cross-sectional shape and sizesubstantially corresponding to distal portions of the first pistonelements 20. The second cup elements 19 likewise have a cross-sectionalshape and size substantially corresponding to distal portions of thesecond piston elements 21. In the illustrated construction, piston rings74 are used to provide a substantially fluid tight sealing relation.However, it is also contemplated that piston rings 74 may be eliminatedif a sufficient direct sealing relation can be achieved.

Regardless of whether or not piston rings 74 are utilized, the first cupelements 18 circumferentially surround distal portions of correspondingfirst piston elements 20 such that the first piston elements 20cooperate with interior boundary walls of the first cup elements 18 todefine a plurality of variable volume first compression chambers 80.Likewise, the second cup elements 19 circumferentially surround distalportions of corresponding second piston elements 21 such that the secondpiston elements 21 cooperate with interior boundary walls of the secondcup elements 19 to define a plurality of variable volume secondcompression chambers 81. As rotatable shaft assembly 12 rotates aroundthe first axis 13, a corresponding circumferential rotation is impartedto the first rotatable piston support 22 and to the second rotatablepiston support 23. As the first rotatable piston support 22 and thesecond rotatable piston support 23 rotate around the first axis 13, thefirst piston elements 20 and the second first piston elements 21 imparta circumferential pushing force to the engaged first cup elements 18 andsecond cup elements 19 thereby causing the first carrier plate 44 andthe second carrier plate 45 to rotate circumferentially. Due to theorientation of the swashplate structure 14, the first carrier plate 44and the second carrier plate 45 rotate around the second axis 15 inangled relation to the first axis 13. Due to the different axis ofrotation, during the rotational cycle, the first cup elements 18reciprocate relative to the first piston elements 20 and the second cupelements 19 reciprocate relative to the second piston elements 21. Thisreciprocating action gives rise to changes in the volumetric capacity ofthe first compression chambers 80 and the second compression chambers81. In this regard, the volumetric capacity cycles progressively betweena high capacity filling stage with the first piston elements 20 and thesecond piston elements 21 substantially withdrawn as shown in the upperleft and lower right portions of FIG. 1 and a low capacity expulsionstage with the first piston elements 20 and the second piston elements21 substantially fully inserted as shown in the upper right and lowerleft portions of FIG. 1. At the low capacity expulsion stage the firstfluid passageways 26 and the second fluid passageways 27 become alignedwith first outlet ports 84 and second outlet ports 85 thereby allowingthe fluid to be expelled in a pressurized state. The flows from thefirst outlet ports 84 and the second outlet ports 85 may thereafter becombined to form a single fluid stream if desired. The floatingengagement between the curved surface support elements and the beveledor curved engagement surfaces allows for naturally occurring minortilting adjustments during the rotational cycle.

INDUSTRIAL APPLICABILITY

The industrial applicability of the pump assembly described herein willbe readily appreciated from the foregoing discussion. Pump assembliesconsistent with the present disclosure may be used to convey fluidsthrough various systems in an efficient manner while maintaining properoperative relation of the various components. By way of example only,and not limitation, exemplary fluids conveyed by the pump assembly mayinclude lubricants, hydraulic fluids, cooling fluids and the like.

In practice, a pump assembly consistent with this disclosure may beutilized in environments such as industrial equipment, transportationvehicles and the like where substantial durability is required. In suchenvironments, a self-balancing swashplate structure supporting anarrangement of cup elements engaging piston elements on either side ofthe swashplate structure may tend to balance forces and promotestability of operation.

It will be appreciated that the foregoing description provides examplesof the disclosed system and technique. However, it is contemplated thatother implementations of the disclosure may differ in detail from theforegoing examples. All references to examples herein are intended toreference the particular example being discussed at that point and arenot intended to imply any limitation as to the scope of the disclosureor claims more generally. Accordingly, this disclosure contemplates theinclusion of all modifications and equivalents of the subject matterrecited in the appended claims as permitted by applicable law. Moreover,any combination of the above-described elements in all possiblevariations thereof is contemplated unless otherwise indicated herein orotherwise clearly contradicted by context.

1. A pump assembly comprising: a tilted swashplate structure; a firstplurality of cup elements projecting away from a first side of saidswashplate structure and a second plurality of cup elements projectingaway from a second side of said swashplate structure facing away fromsaid first side, said swashplate structure being disposed between afirst plurality of piston elements and a second plurality of pistonelements; said first plurality of piston elements projecting away from afirst rotatable piston support towards said first side of saidswashplate structure, at least one member of said first plurality ofpiston elements matedly engaging at least one member of said firstplurality of cup elements; said second plurality of piston elementsprojecting away from a second rotatable piston support towards saidsecond side of said swashplate structure, at least one member of saidsecond plurality of piston elements matedly engaging at least one memberof said second plurality of cup elements; at least one of said firstrotatable piston support and said second rotatable piston support beingadapted to rotate about a first axis, and at least one of said firstplurality of cup elements and said second plurality of cup elementsbeing adapted to rotate about a second axis in angled relation to saidfirst axis.
 2. The pump assembly as recited in claim 1, wherein at leastone of said first rotatable piston support and said second rotatablepiston support is disposed about a rotatable shaft assembly extendingalong said first axis.
 3. The pump assembly as recited in claim 2,wherein each of said first rotatable piston support and said secondrotatable piston support is disposed about said rotatable shaft assemblyextending along said first axis.
 4. The pump assembly as recited inclaim 1, wherein said swashplate structure is supported in pivotingrelation relative to a rotatable shaft assembly extending along saidfirst axis.
 5. The pump assembly as recited in claim 4, wherein at leastone of said first plurality of cup elements and said second plurality ofcup elements is supported at a carrier plate disposed adjacent saidswashplate structure, said carrier plate including an opening disposedcircumferentially about said rotatable shaft assembly, said openingbeing positioned axially along said rotatable shaft assembly inoverlapping relation to at least a portion of a convex surface of acurved surface support element, said opening having a diameter greaterthan a leading edge of said curved surface support element and includinga beveled or curved engagement surface adapted to slidingly engage saidconvex surface of said curved surface support element.
 6. The pumpassembly as recited in claim 5, wherein said curved surface supportelement is non-integral with said rotatable shaft assembly.
 7. The pumpassembly as recited in claim 6, wherein said curved surface supportelement is held in non-rotatable relation relative to said rotatableshaft assembly, such that rotation of said rotatable shaft assembly istranslated to said curved surface support element.
 8. The pump assemblyas recited in claim 7, wherein said curved surface support elementincludes an interior portion adapted to engage a cooperating splinedsurface of said rotatable shaft assembly.
 9. The pump assembly asrecited in claim 8, wherein said interior portion of said curved surfacesupport element includes a pattern of grooves, and said cooperatingsplined surface of said rotatable shaft assembly includes a pattern ofridges adapted to engage said grooves.
 10. The pump assembly as recitedin claim 8, wherein said interior portion of said curved surface supportelement includes a pattern of ridges, and said cooperating splinedsurface of said rotatable shaft assembly includes a pattern of groovesadapted to engage said ridges.
 11. The pump assembly as recited in claim7, wherein said leading edge of said curved surface support elementprojects towards said swashplate structure and wherein said curvedsurface support element is continuously biased towards said swashplatestructure.
 12. A pump assembly comprising: a tilted swashplatestructure; a first plurality of cup elements projecting away from afirst side of said swashplate structure and a second plurality of cupelements projecting away from a second side of said swashplate structurefacing away from said first side, said swashplate structure beingdisposed between a first plurality of piston elements and a secondplurality of piston elements, said first plurality of cup elements beingmounted at a first carrier plate disposed adjacent the first side ofsaid swashplate structure, said second plurality of cup elements beingmounted at a second carrier plate disposed adjacent the second side ofsaid swashplate structure; said first plurality of piston elementsprojecting away from a first rotatable piston support towards said firstside of said swashplate structure, at least one member of said firstplurality of piston elements matedly engaging at least one member ofsaid first plurality of cup elements; said second plurality of pistonelements projecting away from a second rotatable piston support towardssaid second side of said swashplate structure, at least one member ofsaid second plurality of piston elements matedly engaging at least onemember of said second plurality of cup elements; said first rotatablepiston support and said second rotatable piston support each beingdisposed about a rotatable shaft assembly extending along a first axisand each of said first rotatable piston support and said secondrotatable piston support being rotatable around said first axis, saidswashplate structure being supported in pivoting relation relative tosaid rotatable shaft assembly, and each of said first carrier plate andsaid second carrier plate being rotatable about a second axis in angledrelation to said first axis.
 13. The pump assembly as recited in claim12, said first carrier plate being supported at a convex surface of afirst curved surface support element, said first curved surface supportelement being disposed circumferentially about said rotatable shaftassembly, said second carrier plate being supported at a convex surfaceof a second curved surface support element, said second curved surfacesupport element being disposed circumferentially about said rotatableshaft assembly, said first carrier plate including a first carrier plateopening disposed circumferentially about said rotatable shaft assembly,said first carrier plate opening being positioned axially along saidrotatable shaft assembly in overlapping relation to at least a portionof said first curved surface support element, said first carrier plateopening having a diameter greater than a leading edge of said firstcurved surface support element and including a beveled or curvedengagement surface adapted to slidingly engage said convex surface ofsaid first curved surface support element said second carrier plateincluding a second carrier plate opening disposed circumferentiallyabout said rotatable shaft assembly, said second carrier plate openingbeing positioned axially along said rotatable shaft assembly inoverlapping relation to at least a portion of said second curved surfacesupport element, said second carrier plate opening having a diametergreater than a leading edge of said second curved surface supportelement and including a beveled or curved engagement surface adapted toslidingly engage said convex surface of said second curved surfacesupport element.
 14. The pump assembly as recited in claim 13, whereineach of said first curved surface support element and said second curvedsurface support element is non-integral with said rotatable shaftassembly.
 15. The pump assembly as recited in claim 14, wherein each ofsaid first curved surface support element and said second curved surfacesupport element is held in non-rotatable relation relative to saidrotatable shaft assembly, such that rotation of said rotatable shaftassembly is translated to each of said first curved surface supportelement and said second curved surface support element.
 16. The pumpassembly as recited in claim 15, wherein each of said first curvedsurface support element and said second curved surface support elementincludes an interior portion adapted to engage a cooperating splinedsurface of said rotatable shaft assembly.
 17. The pump assembly asrecited in claim 15, wherein said leading edge of said first curvedsurface support element projects towards said first side of saidswashplate structure and said first curved surface support element iscontinuously biased towards said first side of said swashplate structureand wherein said leading edge of said second curved surface supportelement projects towards said second side of said swashplate structureand said second curved surface support element is continuously biasedtowards said second side of said swashplate structure.
 18. A method forpumping a fluid, the method comprising the steps of: providing saidfluid to a pump having a tilted swashplate structure defining a backingsupport for a first plurality of cup elements projecting away from afirst side of said swashplate structure and a second plurality of cupelements projecting away from a second side of said swashplate structurefacing away from said first side, said first plurality of cup elementsmatedly engaging a first plurality of piston elements, said secondplurality of cup elements matedly engaging a second plurality of pistonelements; introducing at least a portion of said fluid into said firstplurality of cup elements and said second plurality of cup elements;reciprocating said first plurality of cup elements and said secondplurality of cup elements relative to the matedly engaged pistonelements; and expelling said fluid in a pressurized state.